1. Field of the Invention
This invention relates to lightweight structural panels and, in particular, to structural panels ideally suited for use as overhead garage doors and to a method for their manufacture.
2. Description of the Prior Art
Structural panels which have, heretofore, been used for garage doors in residential housing have been formed with wood framing and internal bracing and covered on one or both sides with heavy exterior plywood or similar construction material. This results in heavy and massive doors which require massive springs and hinges for their operation. The stiffness-to-weight ratio of the materials employed in construction of such doors is generally inadequate to provide a panel which resists sagging or bending when supported in the open, horizontal position on hinges located at the opposite ends of the panel. Accordingly, most of the panels must be additionally braced by truss rods which extend between the opposite ends of the door, thereby adding to the complexity and weight of the panel. The massive springs employed to balance the door so that it can be readily opened are a hazard to persons and property since failure of the springs or the associated hardware often results in hardware fragments being projected into the garage.
Although it has been generally desirable to provide a lighter weight panel that would be useful as a garage door, heretofore such attempts have been frustrated by the severe use conditions of garage doors. Such panels must be strong and rigid and durable under climatic extremes which include subfreezing temperatures and tropical heat and humidity. The panels should have a high shock and impact resistance to avoid failure upon prolonged use as well as to resist the pounding of tennis balls, basketballs and the like, since these doors are commonly used as backstops in children's play. The door structure should also be rigid in the vertical position and should be rigid and nonsagging when supported overhead from its opposite ends, preferably without the employment of truss rods and similar hardware.